Any guideance to help with .308 problem?

[tllstaco]

I have a .308 AR-10 style rifle that I bought from an individual. Initially, it shoots great but after 40 rounds I begin to have light strikes on the primer. It appears the reason is the bolt is not moving forward completely and therefore not locking in completely. I can use the manual assist knob and push the bolt forward and the rifle fires fine. However, I shouldn't have to use the manual assist knob every shot when it gets hot.

I took the rifle apart, cleaned everything, and oiled/greased it up. Manually cycling the bolt there is a noticeable resistance as the bolt rotates into the locked position. The lugs on the bolt show a little wear (finish is missing) on the back side.

I am new to this style rifle and was wondering if anyone had any advice to help me improve the reliability.

tllstaco

 

[Dawico]

Did you take the bolt carrier apart?

Also, I sometimes use a shotgun bristle brush in a cordless drill to scrub the crap out of the front of the bolt lugs in the barrel. Apply liberal amounts of cleaner to try to loosen up the baked on crap.

 

[tllstaco]

Did you take the bolt carrier apart?

Also, I sometimes use a shotgun bristle brush in a cordless drill to scrub the crap out of the front of the bolt lugs in the barrel. Apply liberal amounts of cleaner to try to loosen up the baked on crap.

Yep, took apart the bolt carrier and cleaned the heck out of it. It's done this since it was new. I'll give the bristle brush a try. Thanks!

tllstaco

 

[Southpaw]

Not saying that this is your exact problem, but I had the similar symptoms with a out of spec bolt on an AR15 (Not sure how different the 10 and 15 are). I bought a new bolt and it works like a charm. I found a marking on the carrier and typed it into Google and found out I wasn't the only one who had issues.

 

[grumper]

Is the gas tube lined up right with the carrier key?

If it's crooked it might cause just enough friction to prevent it from going fully into battery.

 

[Dawico]

Is the gas tube lined up right with the carrier key?

If it's crooked it might cause just enough friction to prevent it from going fully into battery.

That area could be gunked up also causing the same thing.

 

[tllstaco]

Is the gas tube lined up right with the carrier key?

If it's crooked it might cause just enough friction to prevent it from going fully into battery.

That was one of the first things I noticed when it was new. I bought the necessary tools and fixed that little issue. :-) This rifle is teaching me quite a bit about the AR platform. :-)

tllstaco

 

[PhulesAu]

Don't forget to mention Brand name parts if you know them. It might be a well known issue, maybe! What lube did you use?

 

[rsayloriii]

My first suspect would be carbon buildup. Next would be an out of spec component. Something is causing tolerances to become too tight once the metal starts to heat up. I've used carb cleaner (they sell a gun brand of cleaner to do it, but it's the same stuff only more expensive) to make sure there aren't any parts with built up carbon on them. Spray it around the barrel lugs and around and in the gas tube. Use a brush to help get anything left off. Once dry, apply a good lube thoroughly. I personally prefer Frog Lube. It works wonders and makes things just act smoother. Best lube I've ever used.

 

[tllstaco]

Don't forget to mention Brand name parts if you know them. It might be a well known issue, maybe! What lube did you use?

Oops! The upper and lower receiver are by SI Defense. The remainder of the parts are DPMS. As for lube, I have tried 3: Hoppe's Elite, FP-10, and TW25B synthetic grease (based of a recommendation).

tllstaco

 

[tllstaco]

Not saying that this is your exact problem, but I had the similar symptoms with a out of spec bolt on an AR15 (Not sure how different the 10 and 15 are). I bought a new bolt and it works like a charm. I found a marking on the carrier and typed it into Google and found out I wasn't the only one who had issues.

Thanks, I'll give that a try tomorrow.

tllstaco

 

[shortround]

First time, every time, is to check the buffer and recoil spring.

 

[PhulesAu]

Too me it doesn't sound like a "lube" problem. FWIW Do you have a way to check buffer tube for scarring/wear marks?

 

[Leper]

Try a different bcg.

 

[tllstaco]

First time, every time, is to check the buffer and recoil spring.

I'm learning about this rifle. How do you check the buffer and recoil spring?

tllstaco

 

[tllstaco]

Too me it doesn't sound like a "lube" problem. FWIW Do you have a way to check buffer tube for scarring/wear marks?

I don't have a camera or anything. Is there another way to check? I'll try a flashlight and see what I can find.

tllstaco

 

[tllstaco]

Took the rifle apart today and noticed a few interesting things. The threads where the buffer tube screw into the lower receiver had been damaged (completely removed) on two spots on the bottom. These lined up perfectly with two wear marks on the bottom of the bolt carrier. Guess the spring is not keeping the bolt carrier for moving rearward too far. Also, the edges of the buffer on the side where the bolt carrier touches it appears to have been "chipped" away. I'm assuming it should be completely smooth and flat.

I asked the builder if it had the proper buffer spring and was reassured that it did. I'm thinking the answer is it does not. What does everyone think?

 

[Stumpnav]

What brand barrel and gas block/front sight base?

 

[tllstaco]

What brand barrel and gas block/front sight base?

DPMS

tllstaco

 

[Stumpnav]

I worked on a guys DPMS AR that would fail to feed, extract and fire. I chased everything and finally fixed it when I changed out the gas block for a non-DPMS one. It's worked like a champ ever since.

Might look at at the gas block if nothing else works.